A piston-type check valve having an internal diffuser is a known product. A typical example is shown in FIG. 1. More particularly, it involves:
an outer valve body forming a longitudinally extending, through passage and an internal annular seat at its upstream end; PA1 the body is typically of the type known as a "full" body and has end flanges for bolting to end flanges in the line in which the valve is to be used; PA1 a diffuser is centrally mounted in the body passage. The diffuser comprises a hollow, tear/drop-shaped body which combines with the inner surface of the valve body to form an annular, streamlined flow passageway. A piston, comprising a disc and a shaft, is positioned centrally of the diffuser body. The disc is located at the upstream end of the diffuser body and seals against the seat in the closed position. The shaft is guided by a central guide member carried by the diffuser body, so that the piston travels along the long axis of the body. When the piston is displaced from the seat by fluid pressure, it opens the flow passageway. A spring is provided to normally urge the piston to the closed position. PA1 forming the downstream end of the diffuser body/guide member unit so as to provide an axial recess; PA1 mounting an annular tail member on the downstream end of the piston shaft, which tail member retracts into the recess when the piston is in the closed position. The tail member cooperates with the diffuser body to form a substantially continuous extension thereof when the piston is in the open position. The valve body downstream end face may be made substantially flush with the downstream end face of the tail member in the closed position, so that the tail member projects downstream, beyond the valve body end face, when in the open position; and PA1 preferably dimensioning the tail member so that there is a clearance between its outer circumferential surface and the recess surface, for the escape of fluid out of the recess when the tail member is retracting into the recess on the closing stroke. Preferably, and in addition, a dump passage is formed through the diffuser body/guide member unit, commencing part way along the length of the recess and connecting the recess with the downstream end of the passageway. As a result of this construction, fluid may escape readily from the recess through both the clearance and dump passage in the initial portion of the closing stroke, but is metered by the clearance alone in the final portion of the stroke after the tail member blocks the dump passage, to thereby dampen or retard the piston in this final stage of closing and reduce closing impact.
Valves of this type are characterized by a low pressure drop.
It would be desirable to shorten the length of the valve, to reduce its cost and provide it with a short face-to-face dimension, so that it can be used in confined space or as a wafer valve.
It is the objective of this invention to provide a valve design characterized by a reduced body length.